The invention relates to a rotary shaft seal with two diaphragm bodies that are mounted on a support element and display separated sealing diaphragms with sealing lips, which rest against the shaft to be sealed.
Shaft sealing systems involving rotary shaft seals, in which the sealing lip of a sealing diaphragm is inclined against the pressure direction and rests against the shaft to be sealed, are known from EP-A1-07 06 001, for example. Two sealing diaphragms are frequently combined in a sealing system, e.g. when a reserve seal is desired for the event that the first seal fails, e.g. due to particles getting caught between the sealing lip and the shaft. Instead of merely providing a series of simple systems, integrated systems with two sealing diaphragms have also been proposed to achieve a small height. A system of this kind is described in the above European patent application. In this case, a first sealing diaphragm of a first diaphragm body is supported by a pressure mount and a second diaphragm body containing a support element is inserted from the pressure side into the first diaphragm body (see FIG. 2).
A disadvantage of this arrangement is that a gap exists on the pressure side between the first, outside diaphragm body and the second, inside diaphragm body, which can open to form ducts under the effect of the pressurized fluid, thus eliminating the sealing effect of the second sealing diaphragm. This problem becomes particularly serious when particles penetrate the ducts and stabilise them.
The object of the invention is to disclose a rotary shaft seal with two sealing lips that does not display this disadvantage.
The object is solved by a rotary shaft seal as defined in the main claim.
In the seal according to the invention, the gap between the first, inside diaphragm body and the second, outside diaphragm body is covered on the pressure side by the second sealing diaphragm and sealed by the pressure acting on it. Fluids or particles can no longer penetrate the gap.
The support element is preferably designed as an angle ring, whose radial leg faces the second sealing diaphragm and supports it.
The pressure mount also acts as a locking ring by holding the inside parts of the seal in the second, outside diaphragm body. It is preferably of disk-shaped design.
Support element and pressure mount are made of a solid material, such as a metal like steel or special steel.
The diaphragm bodies are preferably made of an elastic material, such as an elastomeric plastic. Particularly suitable are: fluoroelastomers, such as VITON (ISO code FPM), and nitrile rubber, which can be hydrogenated if necessary, such as THERBAN (ISO code HNBR). These elastomers can be cross-linked by the usual methods, such as sulphur or peroxide vulcanization.
The elastomeric material of the sealing diaphragms with the sealing lips, possibly also the entire diaphragm body, preferably contains particles of a lubricating solid. Particularly preferable for this purpose are graphite and polytetrafluoroethylene (PTFE).
The space between the two sealing diaphragms is advantageously filled with a lubricant. This can serve as permanent lubrication, if the fluid medium on the pressure side does not have a lubricating effect, or as emergency lubrication in the event of dry-running.
In a preferred embodiment, a third diaphragm body is provided inside the first diaphragm body and has a sealing diaphragm, whose sealing lip is in contact with the shaft and inclined away from the pressure direction. This diaphragm body seals the container for the fluid medium to be sealed against outside atmospheric pressure when a vacuum prevails in the container, as can be the case (typically 2 to 20 hPa) when filling with medium for the first time. Due to their inclined position, the first and second sealing lips are lifted off the shaft by the outside atmospheric pressure in this case and allow the outside air to enter the container, meaning that filling, e.g. by suction, is prevented or at least greatly delayed.
The sealing diaphragm of the third diaphragm body preferably rests axially against the side of the support element facing away from the pressure. In order to prevent axial shifting in the unpressurised state, the sealing diaphragm of the third diaphragm body is advantageously angled on the outer, radial edge to form an axial leg, which rests against the pressure side of the first diaphragm body. For the purpose of radial mounting, the axial leg is expediently fitted into the first diaphragm body, or possibly in the axial leg of the support element.
The sealing lip of the third diaphragm body is advantageously dimensioned such that it rests against the shaft without pressure. This prevents the third diaphragm body from contributing to the power dissipation caused by friction during operation under pressure.
The third diaphragm body can be made of the same materials as specified above for the first and second diaphragm bodies. However, as it only rests against the shaft under pressure during filling while the shaft is stationary, the material does not need to contain any lubricating solid particles. Simple nitrile-butadiene rubber (NBR) is suitable, for example.
One advantage of the rotary shaft seal according to the invention is that, during assembly, the inside parts can all be inserted into the second, outside diaphragm body from one side, i.e. the unpressurised side. This also applies to the third diaphragm body, if appropriate. This facilitates manufacturing. In the known seal according to FIG. 2, this is not possible due to the T-profile of the outer diaphragm body.
Another advantage in the assembly of the seal according to the invention is that it remains intact when pressed into the bearing mount under axial pressure. The axial pressure is necessary, because the elastic, second diaphragm body is slightly oversized and is secured in the bearing mount by means of a press fit. In the known seal (FIG. 2), the pressure-side diaphragm body can move axially in the other diaphragm body prior to assembly. This poses the risk of it getting caught on the shaft and shifting against the other diaphragm body, so that the seal falls apart or exceeds the specified axial dimensions. The diaphragm body on the pressure side is, at the least, no longer fixed in place and the pressurised medium can pass through the gap between the diaphragm bodies more easily.
The rotary shaft seal according to the invention can be used to seal shaft openings leading into vessels containing a pressurised fluid medium. It is particularly suitable for sealing shafts on water pumps, especially for internal combustion engines in motor vehicles.